As for the disposal of wet sludge, such as sewage sludge, discharged from a sewage disposal plant, the conventional reclamation disposal and ocean disposal have become difficult because of the depletion of disposal site and the restrictions for preventing environmental pollution in recent years. For this reason, there has been also proposed a method for incinerating the wet sludge in an incinerator. However, for example, even the sewage sludge which is formed into a dehydrated cake in the sewage disposal plant contains about 80% moisture.
Therefore, in the disposal method using the incinerator, it is necessary to dry the wet sludge beforehand in order to reduce the thermal load of the incinerator. This results in a problem that the disposal method is inferior in cost effectiveness because additional costs, such as the cost for drying the wet sludge, and the cost for deodorizing the exhaust gas generated during the drying treatment are required in addition to the cost originally required for the incineration.
Thus, in order to solve the above described problem, the present applicants have previously proposed, in Japanese Patent No. 3246509 (Patent Document 1), a wet sludge disposal facility utilizing a cement clinker manufacturing facility.
The patented invention is, as shown in FIG. 5, a wet sludge disposal facility installed in combination with a cement clinker manufacturing facility which includes a preheater 1 for preheating a cement raw material crushed by a raw-material mill, and a dry process kiln 3 connected to the preheater 1 at the kiln inlet part 2 of the dry process kiln 3, for calcining the preheated cement raw material. The wet sludge disposal facility is characterized by including: a sludge tank 4 for storing wet sludge; a pressure feed pump 5 for pressure-feeding the wet sludge in the sludge tank 4; and a pipe 6 connected to the pressure feed pump 5, for directly charging the wet sludge into the dry process kiln 3, and is characterized in that the pipe 6 is connected to the kiln inlet part 2 or a calcining furnace 7.
According to the above described wet sludge disposal facility, wet sludge, such as sewage sludge, is directly charged into the existing dry process kiln 3 and incinerated in a high temperature atmosphere of 800° C. to 1200° C., without applying pretreatment such as drying treatment and additive adding treatment, and without causing a problem of environmental pollution, whereby the final treatment of the wet sludge can be efficiently performed at low cost, and the sludge incineration ash can be economically reused as cement clinker. Further, since the wet sludge is pressure-fed through the pipe 6 so as to be directly incinerated, it is also possible to obtain an effect of preventing the malodor problem and the like.
Meanwhile, for example, when sewage sludge is disposed in the above described disposal facility, the excess moisture of the sewage sludge is usually removed so as to be formed into a dehydrated cake having a moisture content of around 80% in the sewage disposal plant mainly for convenience of transportation, and is then transported to the cement manufacturing plant by a truck.
In the upper part of the sludge tank 4, a large sludge charging port is formed to receive the wet sludge transported by the truck. In the sludge charging port, there is provided a closing cover which is closed except at the time of receiving the sludge transported by the truck, because when the sludge charging port is always opened, malodor and gas may be generated from the surface of the wet sludge in the sludge tank 4, and diffused to the outside so as to deteriorate the working environment. Further, the sludge tank 4 is covered by a building 8, and apparatuses, such as a put-out apparatus of the sludge tank 4, the pressure feed pump 5, and a hydraulic unit 9 for driving the pressure feed pump 5 are installed in the building 8.
However, when the sludge tank 4 is simply covered only by the building 8 or the like, the malodor and gas stagnate in the inner space of the building 8. For this reason, there is a problem that when the gate of the building 8 is opened, for example, in order to allow the truck to enter the building 8, the malodor and gas are discharged to the outside. Further, there is also a problem that when a worker enters the building 8 in order to perform maintenance of the above described apparatuses, the worker is exposed to a poor working environment due to the malodor and the like.
Further, since the sludge tank 4 is always closed by the closing cover, the highly concentrated malodor and the like stagnates in the sludge tank 4. For this reason, there is a problem that when the closing cover is opened at the time of receiving the sludge or at the time of repairing the sludge tank 4, the malodor in the sludge tank 4 is dispersed inside the building 8, to thereby cause a similar harmful effect.
Thus, it is necessary to provide a ventilation system for ventilating the inside of the building 8. However, there is a problem that in order to always perform overall ventilation inside the building 8 and the sludge tank 4 in an air quantity also enabling the discharge of the malodor and the like generated in a large quantity at the time of sludge reception, an outer air blowing fan and an exhaust suction fan, each having an extremely large capacity, are required to thereby cause an increase in the facility costs and operation costs.
Further, depending upon the properties of the sewage sludge and the temperature atmosphere inside the building 8, harmful gases such as methane gas and hydrogen sulfide gas may be generated from the sludge tank 4. Further, the methane gas having a specific gravity smaller than that of air stagnates in the upper part of the building 8, while the hydrogen sulfide gas having a specific gravity larger than that of air stagnates in the lower part of the building 8. For this reason, there is a problem that in order to prevent the stagnation of the gases, a ventilating flow from the lower part to the upper part of the building 8 needs to be always formed by the above described fans having a further larger capacity.
Patent Document 1: Japanese Patent No. 3246509